This is a very old story.
When I was young, playing Xenon 1, I kept telling my brothers that in the meteors noise (level 3), I was hearing lost in the noise a small music, like bells. They claimed they didn't hear anything.
The music consists of 4 notes repeating about every 3 seconds.

This time you should hear "tik tik tik tik" exactly 4 times behind the white noise, just like someone hammering on an anvil or something like that.
This way you might hear how it sounds like and hear it more easily in the very first file.

Can't here the bells but then I've got Tinnitus in both lugholes.
On this subject though, for years I've said to people that one of the Windows startup jingles contains the sound of a woman in the throws of orgasm. Listen to the windows 2000 jingle http://www.youtube.com/watch?v=BFkry3zzutI
It gets a bit gaspy at the end. Tinnitus or not it's deffo there!

kenneth wrote:Perhaps a sound signature of the inventor of the AY?
Some instructions not listed in the 6502 runs correctly, the engineers hide us something...

In fact, it seems related to the way random number are generated. The noise generator is mainly a random function, and since on computer random is never really random, especially on old components, the tictic we ear can be due to some repetitions in the random sequence.

Symoon wrote:This is a very old story.
When I was young, playing Xenon 1, I kept telling my brothers that in the meteors noise (level 3), I was hearing lost in the noise a small music, like bells. They claimed they didn't hear anything.
The music consists of 4 notes repeating about every 3 seconds.

I can just about hear the 'tick tick' thing. Doesn't sound like bells though...
Funnily enough though, I was deaf for 2 days after seeing AC/DC in Dublin and have suffered TInnitus ever since!! Kids - use those earplugs lol... T

Now I'm wondering how these notes are there... Never really dug the subject further, not sure if this is specific to Xenon or the the Oric white noise generation.

kenneth wrote:Perhaps a sound signature of the inventor of the AY?
Some instructions not listed in the 6502 runs correctly, the engineers hide us something...

In fact, it seems related to the way random number are generated. The noise generator is mainly a random function, and since on computer random is never really random, especially on old components, the tictic we ear can be due to some repetitions in the random sequence.

A million years late, as ever, but the random noise generator function for the AY is known — see e.g. this Amstrad CPC wiki.

To reproduce the formulation here just in case other sources drop offline, it's a 16-bit shift register. It shifts at the noise frequency. Upon each shift:

output is XORd with the bit that just fell off the bottom;

the new top bit is the bit that fell off XORd with the bit that just moved from bit 3 to bit 2.

I'm confident the same solution is given independently in this Russian documentation based on the included Pascal code — actually x86 assembly inline in Pascal code — and Google's translated version of the included document, except that they conceptualised the shift register as going to the left instead of the right so talk about bit 13 rather than bit 2.

That's how I implemented it on my emulator and it feels correct. So I'm confident based on (i) subjective listening; and (ii) two almost-certainly independent sources.